As integrated circuit (IC) devices and IC circuits (collectively, IC circuitry--such as digital signal processors (DSPs) and mixed signal analog circuits, for example) continue to shrink in size and increase in complexity, more precise control of input voltages and input currents to IC circuitry is required. To control input voltages, modem IC circuitry utilize voltage regulators to insure that a relatively constant input voltage is maintained on the input to the IC circuitry. However, the miniaturization of IC circuitry has progressed to the point where constant input voltage regulation alone is not sufficient to insure the integrity and performance of the IC circuitry.
For example, when an IC circuitry starts-up, if the operational (steady-state) input voltage of the IC circuitry is immediately placed on the IC circuitry input, the IC circuitry may experience an excessive input current. This excessive input current may bum out transistors (called high in-rush current and may cause "over-voltage condition"), place undesired biases in the IC circuitry, and inject free electrons into the substrate of the IC circuitry. To limit the problems caused by an excessive input current, and to control other damaging effects of start-up operation, some regulators use two different regulation states (these are known as dual-mode voltage regulators). For example, one dual-mode voltage regulator uses current sources to place one fixed voltage on the input to the IC circuitry for a brief period of time, called a start-up phase. Then, after the start-up phase is complete, the dual-mode voltage regulator places a second fixed voltage (the operational voltage of the IC circuitry) on the input to the IC circuitry.
Unfortunately, the performance of prior-art voltage regulators, including dual-mode voltage regulators, is unsatisfactory and suffers from numerous disadvantages. For example, even small sudden changes in the input voltage can inject noise into the IC circuitry. In addition, though dual-mode voltage regulators reduce the damage caused by placing an operational voltage source directly on an IC circuitry, over-voltage conditions may still occur, free electrons may still be injected into the substrate, and the forwarding of back diodes can still occur. Also, the addition of the start-up phase in dual-mode voltage regulators increases the time it takes for an IC circuitry to become operational, which decreases the performance of the IC circuitry. Furthermore, dual-mode voltage regulators occupy a relatively large amount of IC wafer space. All of these factors contribute to reducing the performance and efficiency of the IC circuitry.
Therefore it is desired to have a voltage regulator circuit and a method for implementing a voltage regulator that provides safe start-up operations, increases start-up speeds, increases IC circuitry efficiency, prevents over-voltage conditions, and reduces the likelihood of noise injection in the IC circuitry, and electron injection into the substrate. The present invention provides such a device and method.